1. Field of the Invention
The present invention relates to a communications method in which a transmitting terminal device transmits data to a receiving terminal device by simultaneously using a plurality of paths, and relates to communication terminal devices which realize the communications method.
2. Description of the Related Art
Techniques cited in a Non-patent Document 1 (RFC2960, “Stream Control Transmission Protocol (SCTP)”), a Non-patent Document 2 (“A transport layer approach for improving end-to-end performance and robustness using redundant paths”, Arvind Krishnamurthy, Larry Peterson, Ming Zhang, Junwen Lai, Randolph Wang, USENIX '04, pages 99-112, June 2004), and a Non-patent Document 3 (“A transport layer approach for achieving aggregate bandwidth on multi-homed mobile hosts”, Hung-Yun Heleh, Raghupathy Sivakumar, ACM Mobicom '02, September 2002) are conventionally known as a communications method which uses a multi-home-capable Transport Protocol (for example, a Multi-Path Transmission Control Protocol (TCP)), that is, a communications method in which a transmitting terminal device transmits data to a receiving terminal device by simultaneously using a plurality of paths.
However, the communications method using the multi-home-capable Transport Protocol, which is proposed in the Non-patent Document 1, is configured to use only a single path which is in the best communications status in order to carry out communications and to use another path as an alternative path upon failure.
Therefore, there is a problem that it is not possible to carry out communications by simultaneously using a plurality of paths.
On the other hand, the techniques proposed in the Non-patent Documents 2 and 3 can carry out communications by simultaneously using a plurality of paths which exist between a transmitting terminal device and a receiving terminal device.
However, the technique proposed in the Non-patent Document 2 requires a new header over a normal TCP header. Thus, there is a problem that it is not possible to carry out communications with communication terminal devices without a protocol proposed in the Non-patent Document 2.
Regarding this point, the technique proposed in the Non-patent Document 3, is configured to realize communications by simultaneously using a plurality of paths existing between transmitting and receiving terminal devices by use of a normal header alone (that is, a multi-home connection).
However, the technique proposed in the Non-patent Document 3 can use only one path for transmitting a receipt acknowledgement signal of Acknowledgement (ACK) (an ACK path).
Therefore, if a failure occurs in the ACK path which is being used, all paths are influenced, and also each path becomes asymmetric (a path which transmits data is different from a path which receives an ACK for the data). Consequently, there is a problem that Round Trip Time (RTP) cannot be measured accurately.
Furthermore, the technique proposed in the Non-patent Document 3 has a problem that it is not possible to use a Cumulative ACK (C-ACK), and the like. In addition, there is a problem that it is not possible to perform control equivalent to a normal TCP by the path unit.